Investigating the effect of Cu-doping on the electrochemical properties of perovskite-type Ba_0.5Sr_0.5Fe_1-xCu_xO_3-δ (0 ≤ x ≤ 0.20) cathodes

The effect of Cu-substitution in Ba_0.5Sr_0.5Fe_1-xCu_xO_3-δ (BSFCux (0 ≤ x ≤ 0.20)) on structure and electrochemical performance was investigated using BSFCux + LSGM|LSGM|BSFCux + LSGM symmetrical cells. Powder X-ray diffraction showed that the lattice constant increased with increasing Cu in BSFCux. The effect of sintering temperature on the oxygen reduction reaction (ORR) was studied for Ba_0.5Sr_0.5Fe_0.95Cu_0.05O_3-δ + LSGM and Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3-δ + LSGM symmetrical cells. Ba_0.5Sr_0.5Fe_0.95Cu_0.05O_3-δ + LSGM showed the lowest area specific resistance (ASR) of 0.031 Ωcm² at 800 °C in air when the cell was sintered at 1000 °C. The effect of LSGM thickness was studied on BSFCu0.05 at 1000 °C, which showed minimal effect on the ASR with electrolyte thickness (760–3110 μm). To understand the ORR mechanism of Ba_0.5Sr_0.5Fe_0.95Cu_0.05O_3-δ + LSGM and Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3-δ + LSGM, the data was analyzed using equation [ASR]=[ASR]⁰(pO₂)ⁿ. N values of 0 and 0.125 were obtained for Ba_0.5Sr_0.5Fe_0.95Cu_0.05O_3-δ indicative of O²⁻ incorporation from the triple-phase-boundary (TPB) to the electrolyte and the charge transfer at the TPB as the rate determining steps for the ORR. N values of 0.35 and 0.50 were obtained for Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3-δ indicative of the dissociative charge transfer and the dissociation of adsorbed O₂ as the rate determining steps for the ORR.